Hearth



March 25, 1969 w, G, SHEDD ET AL 3,434,703

HEARTH INVENTiOR-S Wilfred 6. {b309 Fl 0 B BY Bares-fora m. 0/4,

March 25, 1969 w. G. SHEDD ET AL 3,

HEARTH Z of 2 Sheet Filed Dec. 9, 1966 United States Patent US. Cl. 263-21 8 Claims ABSTRACT OF THE DISCLOSURE A hearth for use in a shaker-hearth-type heat treating furnace which has an elongated rigid lattice type frame on which a plurality of pans are arranged successively between the opposite ends of the frame. Each of the pans is secured to the frame adjacent one pan end and all pans except a single pan adjacent to one frame end receives into the other pan end the secured end of the next adjacent pan. Otherwise, the pans are unsecured to the frame. Openings in the frame communicate with the bottom of each of the pans.

The present invention generally relates to a hearth for use in a shaker-hearth-type heat treating furnace, and more specifically relates to a new and novel hearth having a construction which provides not only the desired rigidity but also the property of being free to expand and contract during use without buckling or otherwise deforming.

Several prior hearth designs have been proposed for use with shaker-hearth-type heat treating furnaces. Each of these prior hearths is made of materials which have high strengths at relatively high temperatures, for example, temperatures of between 1000 F. and 2500 F. However, since a hearth in a conventional shaker-hearth-type furnace is not rigidly connected to the furnace but is mounted to be shaken," i.e., alternately abruptly moved in an axial direction and then abruptly stopped thereby to move the work to be heat treated axially along the hearth and through the furnace, the hearth is subjected to a variety of stresses during use. The hearth, itself, must withstand all of these forces including the shaking forces applied thereto by the means moving the hearth and the forces due to the variable cooling of the hearth by the Work thereon.

Each of the prior art hearth designs is defective either because the hearth incurs buckling or other deformation during use, or because the size and weight or the complexity of the design of the hearth requires relatively expensive redesign of the furnace and/or the means driving the hearth, or makes the hearth relatively expensive to manufacture. Therefore, it is highly desirable to provide an improved hearth for use with a shaker-hearth furnace which can be manufactured relatively inexpensively, which is both sufficiently strong and rigid to prevent any substantial buckling or deformation during use, and which can be used with conventional heat treating furnaces without necessitating relatively expensive modification to the furnace or the means driving the hearth.

It is therefore the primary object of this invention to provide an improved hearth which can be used with conventional shaker-hearth-type heat treating furnaces.

Another object of this invention is to provide an improved hearth which has sufficient strength and rigidity to prevent buckling or other deformation during use and which can be used with conventional shaker-hearthtype heat treating furnaces without necessitating relatively expensive modifications to the furnace or to the hearth-driving means provided with the furnace.

Yet another object of this invention is to provide an 3,434,703 Patented Mar. 25, 1969 improved hearth for use in a shaker-hearth-type heat treating furnace which has a suitably rigid and strong frame and work-carrying pans secured to the frame both of which can expand and contract freely Without buckling or otherwise deforming any part of the hearth.

A further object of this invention is to provide an improved hearth for use in a shaker-hearth-type heat treating furnace and which has an elongated frame having side members which have sufficient rigidity and strength and a sufiiciently high moment of inertia to resist any deformation of the hearth due to the forces applied thereto by the driving means at furnace operat- I ing temperatures between about 1000 F. and 2500 F.

Still further an object of this invention is to provide an improved hearth for use in a shaker-hearth-type heat treating furnace and having an elongated frame which can expand and contract both longitudinally and transversely thereof without buckling or otherwise being deformed, and further having relatively short work-carrying pans arranged in succession along the length of the frame in an overlapping manner such that the pans can also expand and contract freely in both the directions abovementioned without buckling or otherwise being deformed.

In the broader aspects of this invention there is provided an improved hearth for use in a shaker-hearthtype heat treating furnace and comprising an elongated frame and pan assembly having a bottom and upstanding longitudinally extending sides forming an open top and opposite open ends. The frame of the assembly is rigid and of a lattice type and has two longitudinally extending side members which are spaced apart and generally parallel. Each of the side members define the upstanding sides and the bottom of the assembly and are rigidly connected together by a plurality of transverse members extending between the side members. The frame bottom has openings therein and a plurality of pans are assembled on the frame bottom between the upstanding sides thereof. The pans are arranged in succession and in a shingle-like manner between the opposite frame ends. Each of the pans is secured adjacent to one end thereof to the frame bottom; the other end of each of the pans is unsecured. The openings in the frame bottom communicate with the bottom of the pans thereby eliminating any dead space in the frame and pan assembly. The pans are spaced from the upstanding frame sides whereby both the pans and frame of the assembly are free to expand and contract both longitudinally and laterally of the assembly without buckling or otherwise deforming the pans or frame of the assembly.

The above-mentioned and other features and objects of this invention and the manner of attaining them will become more apparent and the invention itself will be best understood by reference to the following description of an embodiment of the invention taken in conjunction with the accompanying drawings, wherein:

FIG. 1 is a side view, partially in cross-section and partially diagrammatic, of a shaker-hearth-type heat treating furnace having the improved hearth of this invention mounted therein and connected to means for moving the hearth in a conventional manner;

FIG. 2 is a top view of the hearth of this invention;

FIG. 3 is a cross-sectional view of the hearth illustrated in FIG. 2 taken substantially along the section line 3-3 thereof;

FIG. 4 is a cross-sectional view of the hearth illustrated in FIG. 2 taken substantially along the section line 44 thereof and showing the attachment of the pans of the hearth to the frame;

FIG. 5 is a fragmentary side view of the hearth illustrated in FIGS. 2, 3 and 4; and

FIG. 6 is a perspective view of one of the pans of the hearth of this invention.

Referring to the drawings, and more specifically to FIG. 1, there is shown a shaker-hearth-type of heat treating furnace having the improved hearth 9 of this invention mounted therein. Such furnaces 10 are conventionally supported upon a base 12 which may be elevated from the floor by suitable legs 14. Mounted on the base 12 is a furnace bottom 16 which is suitably insulated from the frame 12 by insulation 18. conventionally the furnace bottom 16 is lined with firebrick 20. Mounted on the firebrick 20 is a hearth-supporting structure 22 which in the preferred embodiment of this invention is a skid comprising a plurality of rails upon which the hearth of this invention rests. The structure 22 supports the hearth within the furnace and the hearth is slideable on the support 22. Also supported on the base 12 is a hydraulic fluid reservoir 24, a compressor 26 which functions to maintain the pressure of the fluid within the reservoir 24 and a timing mechanism 28, the purpose of which will be mentioned hereinafter. Secured to the hearth 9 of this invention exterior of the furnace 10 is a member 30 which is secured to a piston (not shown) in a double acting hydraulic cylinder 32. interconnecting the cylinder 32 and the reservoir 24 are a pair of conduits 36, 38. Conduits 36 and 38 communicate with cylinder 32 on opposite sides of the piston therein. Within the conduits 36 and 38 are solenoid valves 42 each of which is operated by the timing mechanism 28, aforementioned. Thus, the timing mechanism 28, appropriately set, controls the movement of the hearth within the furnace 10. The remainder of the furnace 10 comprises a backwall portion 44 and a top portion 46, and obviously, opposite side portions (not shown). Both the backwall portion 44 and the opposite side portions are lined with firebrick 20 and appropriately insulated as at 48. Top 46 has a recess 50 therein in which an appropriate number of heating elements 52 are positioned.

In operation, the hydraulic cylinder 32 is operated by the timing mechanism 28 to drive the hearth 9 in the direction of the arrow 54 and to abruptly stop the hearth thereby to move the work on the hearth axially of the hearth. Since there is a temperature differential within most furnaces such as that above described, the work may be moved toward the discharge end of the hearth a partial distance of the hearth and then reversed in direction, and subsequently again reversed in direction to give the work, the desired heat treatment. While the forces applied to the hearth 9 to drive and to abruptly stop the hearth are desirably applied to the hearth 9 in an axial direction, in practice, this is diflicult to accomplish, and thus, the driving means most always imparts to the hearth 9 a force which tends to deform the hearth, buckle or bend the hearth 9.

Referring specifically to FIGS. 2 through 6, the improved hearth of this invention will now be described. Hearth 9 comprises an elongated frame and pan assembly 56 having a bottom 60 and upstanding longitudinally extending sides 62 and 64. The assembly 56 has an open top 66, an open discharge end 68 and an open opposite end 70. The assembly comprises a rigid and elongated lattice type frame 72 and a plurality of pans 74. Frame 72 has two side members 75 and 76, each of which extends longitudinally of the frame 72. Side members 75 and 76 are spaced apart and generally parallel to each other. Each side member 75, 76 has two longitudinally extending flange portions 78, 80 and an L-shaped crosssection. One flange portion 78 of each of the members 75 and 76 extend toward each other thereby forming the assembly bottom 60.

The other flange portions 80 upstand from the bottom 60 thereby forming the opposite longitudinally extending sides 62, 64 of the assembly 56. Side members 75 and 76 are rigidly connected together by a plurality of transverse members 82 extending between the side members. This frame 72 as above described has openings 84 therein between the members 82.

Assembled on the frame 72 and between the flange portions are a plurality of pans 74 each of which is identical except for the dimensions measured axially of the frame 72. Thus a description of one pan 74 will suffice for all. Each pan 74 has a bottom 86, upstanding opposite sides 88, 90, an open top 92, and opposite open ends 94 and 96. Pan bottoms 86 are tapered, and pan ends 96 are wider than pan ends 94. Pan sides 88, 90 are not parallel and taper toward each other from pan end 96 to pan end 94. Pan ends 96, 94 and the crosssection of pan 74, such as that illustrated in FIG. 3, each have a rectangular shape.

Each pan 74 on the frame 72 has its end 84 most adjacent discharge end 68 and its larger end 96 most adjacent end 78. The portion of each pan 74 adjacent end 94 overlays the portion of the next adjacent pan '74 adjacent to pan end 96. Thus, pans 74 adjacent ends 94 are telescoped into the next adjacent pan 74 adjacent ends 96 and are positioned between the opposite upstanding sides 88, 90 thereof. This is what is meant hereinabove and in the claims by the term shingle-like when used to describe the assembly of the pans 74. Further, each of the pans 74 is secured to the frame 72 adjacent to end 96. The preferred attachment of the pans 74 to the frame 72 is shown in FIG. 4. The structure attaching the pans 74 comprises a member 108 which extends longitudinally of each member 82 and is secured thereto. Member 100 has a thickness slightly larger than the pan bottom 86. The pan 74 adjacent end 86 is secured to the member 100 thereby leaving a space 102 between the flange portions 80 of the frame 72, the pan bottom 86 of the last-mentioned pan, and the member 82 such that the portion of another pan adjacent an end 94 thereof can be positioned therein. This structure allows for the overlapping and the shingle-like assembly of the pans 74 within the frame 72, as above described. The pan end 94 is positioned within space 102 in spaced apart relation to member thereby leaving a space 104 for longitudinal expansion of each pan 74 adjacent to end 94 thereof. This space 104, however, is not a dead air space in the pan and frame assembly 56 since each end of the space 104 is open. In fact, the pan and frame assembly 56 does not have any dead air spaces therein since the openings 84 communicate with the pan bottom 86 as shown in FIG. 2. Further, since each of the pans 74 are spaced apart from the opposite flange portions 88 of the frame 72, and the space 104 is left between each pan end 94 and member 100, and pan ends 94 are not secured to the frame 72, pans 74 are free to expand within the frame 72 both longitudinally and laterally thereof.

Referring now back to the frame 72, and to FIGS. 2, 3 and 5 illustrating the same, it should be understood that the rigidity and strength of the frame 72 is substantially derived from the L-shaped side members 75 and 76. Members 82 primarily attach the members 75, 76 together and do not substantially add to the rigidity of the frame 72 or substantially prevent the frame 72 from expanding longitudinally thereof. Thus, frame 72 is also free to expand and contract both longitudinally and laterally thereof. However, for this reason, members 75, 76 are provided with sufficient rigidity and strength to resist any bending moment or other forces applied to the pan and frame assembly by the means above described which drives and abruptly stops the assembly during use. Since most of the frame and pan assembly 56 is at elevated temperatures, the strength and rigidity must be such that no deformation, buckling, bending or the like occurs at the furnace temperatures which range, during operation, between about 1000 F. and about 2500 F. A substantial portion of the rigidity of the frame 72 is derived from providing members 75, 76 with a moment of inertia about any axis about which deformation is likely to occur which is sufficiently large to solely resist any dynamic deformation of the frame 72 caused by the means which drives and abruptl stops the hearth of this invention.

In a specific embodiment of this invention, the pan and frame assembly has the following dimensions:

Frame 72:

Length 10", Width 18.5". Members 75, 76:

Flange 78, 80-thickness -e Flange 78, 80-width 3". Flange 78, git-length 1510. Members 82:

Length 18.5". Width 3". Thickness Members 100:

Length 16.5". Width 1". Thickness Pans 74:

Length Varies from 33" to 62". Width at end 96 17". Width at end 94 16.25". Depth 2. Thickness /8".

Frame 72 and pans 74 are made of a chromium and nickel alloy steel and the respective members of the frame 72 and the pans 74 and the frame 72 are secured together by welding.

In operation, the hearth 9 of this invention is supported within a conventional furnace 10 such as that shown in FIG. 1 on the hearth supporting device 22. The means aforedescribed for driving the hearth 9 is attached to the frame 10 by welding the member 30 to the hearth 9 adjacent end 70. The work desirably treated by the furnace 10 is placed upon the hearth 9 adjacent end 70 exterior of the furnace 10 and the motion of the hearth 9 moves the work axially along the hearth 9 toward the discharge end 68. At this point, the work is deposited onto the conveyor 110 which conveys the work in the direction of the arrow 112 to further treatment which may be quenching and the like.

The improved hearth of this invention because of its unique construction resists buckling, bending or other deformation of the hearth during use. Thus, the hearth 9 of this invention can be used over a prolonged period of time without replacement. During use, the hearth 9 will undergo erratic temperature changes both due to the movement of the hearth 9 and the cooling thereof by the work thereon. The unique construction of the hearth 9 of this invention allows both the frame 72 and the pans 74 to expand or contract in accordance with the changing temperature of the respective parts of the hearth 9 either longitudinall or laterally of the frame 72 or in both directions. This allows the hearth 9 to accommodate such temperature changes without deformation. Further, since there are no dead air spaces within the structure of the hearth 9, it changes temperature quickly, and thus, stresses due to the same part having a temperature gradient are minimized. All of this prolongs the life of the hearth 9 when in use.

Further, the hearth 9 of this invention provides a frame 72 which is suitably strong to resist any forces placed thereon by the means driving the hearth 9. This is accomplished in the hearth of this invention without adding materially to the size and weight of the hearth such that conventional driving means can be used and conventional furnaces need not have extensive modifications in order to use the hearth of this invention.

Still further, the structure of the hearth 9 is simple and unencumbered with unnecessary structural members. This allows the hearth of this invention to be manufactured relatively inexpensively.

While there have been described above the principles of this invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of the invention.

What is claimed is:

1. A hearth for a shaker-hearth-type heat treating furnace comprising an elongated frame and pan assembly having a bottom and upstanding longitudinally extending sides, said assembly having an open top and opposite open ends, a rigid and elongated frame having two side members extending longitudinally thereof, said side members being spaced apart and generally parallel to each other, said side members being rigidly connected together by a plurality of transverse members extending between said side members, said transverse members defining a frame bottom, each of said side members having a longitudinally extending member portion, said member portions upstanding from said frame bottom, said frame bottom having openings therein, said openings comprising a substantial portion of the area of said frame bottom, and a plurality of pans assembled on said frame between said member portions, said pans being arranged in succession and in an overlapping shingle-like manner between said opposite frame ends, means for connecting each of said pans to said frame with said pans spaced from said frame, each of said pans being secured to said frame adjacent to one end thereof, the other of said pan ends being held to said frame by the next adjacent of said pans, the other of said pan ends of each of said pans being slidable in relation to said frame and said next adjacent pan upon longitudinal expansion of said pan, said openings in said frame bottom communicating with said pans, whereby said assembly has no dead air spaces therein, and said pans and frame are free to expand and contract both longitudinally ard laterally of said assembly without distorting said assembly.

2. The hearth of claim 1 wherein said side members have a moment of inertia about a transverse axis which is larger than the moment of inertia about a corresponding axis of a member having the same cross-sectional area as said side member but having a circular cross-section, said side members being solely suflicient to resist any dynamic deformation of said assembly during use.

3. The hearth of claim '1 further comprising means for driving and abruptly stopping said assembly in a manner which subjects said assembly to a bending moment, and wherein said side members have sufiicient rigidity and strength to resist said bending moment applied to said hearth by said means at furnace temperatures below 2500 F.

4. The hearth of claim 2 wherein each of said pans have a bottom and upstanding sides, said. pans having an open top, said one and other of said pan ends being open, said bottom being tapered between said ends, said other of said pan ends being wider than said one of said pan ends, said pans having immediately adjacent pans on both ends thereof and having a portion of one of said adjacent pans positioned in said other end thereof, and further having a portion thereof adjacent to said one end positioned in said other end of the other adjacent pan, whereby portions of said adjacent pans adjacent to said ends thereof overlap in a manner allowing work to flow from said other pan ends to said one pan ends.

5. The hearth of claim 2 wherein said frame has means including said side members adapting said frame to be supported within a furnace on a skid extending longitudinally of said frame along which said frame is slideable.

6. The hearth of claim 2 wherein said pans adjacent to said one pan ends are secured to said transverse members, respectively, in spaced apart relation thereto, and said other pan ends of said other adjacent pans are positioned between said one pan ends and said transverse members.

7. A hearth assembly for a shaker-hearth-type of furnace comprising: an elongated frame having charge and discharge ends, said frame extending longitudinally between said ends, said frame having a pair of elongated, transversely spaced-apart rigid side members, a plurality of rigid member portions respectively extending transversely between and rigidly joined to said side members, and a plurality of pans each having a flat bottom and upstanding opposite side walls, each of said pans having open forward and rear ends, said side walls of each of said pans converging from the forward to the rear end thereof whereby said rear ends are smaller than said forward ends, said pans being arranged sequentially on said frame between said opposite ends thereof and between said side members with said rear ends facing said discharge end of said assembly and said forward ends facing said charge end of said assembly, each of said pans having its rear end extending into the forward end of the immediately adjacent pan toward said discharge end of said assembly thereby to provide a shingle-like arrangement of said pans, each of said pans being rigidly connected adjacent its rear end to a respective tranvere member portion with its forward end being unsecured to said frame but held to said frame by the immediately adjacent pans, said side walls of each of said pans being spaced from said side members, thereby permitting both transverse and axial expansion of said pans.

8. The assembly of claim 7 wherein each of said transverse member portions has forward and rear sides and an upper surface, said forward sides facing said charge end of said assembly, each of said transverse member por- 8 tions having a transverse element secured to its upper surface, each of said elements having a width less than that of the respective transverse member portion and being secured thereto adjacent its forward side thereby exposing a portion of said upper surface adjacent the rear side, each of said pans other than the pan at said discharge end of said assembly having its bottom adjacent its rear end supported by and secured to a respective element and having its. rear end extending rearwardly of said element and overlying said exposed portion to define a recess therewith, each of said pans other than the pan at the charge end of said assembly having its forward end extending into said recess defined by the rear end of the immediately adjacent pan and being slidably supported on the exposed surface portion of the respective transverse member portion, said forward end being axially spaced from the respective element.

References Cited UNITED STATES PATENTS 2,820,622 1/ 1958 Mescher. 2,940,743 6/ 1960 Walpole. 3,133,628 5/ 1964- Butler et a1.

FREDERICK L. MATTESON, JR., Primary Examiner.

EDWARD G. FAVORS, Assistant Examiner.

U.S. Cl. X.R. 198-220 

